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Mini Spares 5 Spd Trans - .80 5Th Gear?

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#1 bluedragon

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Posted 13 January 2017 - 11:07 AM

The current exchange rates have got me thinking about the Mini Spares 5 speed helical gearbox. I have to agree with many other opinions that it's only a marginal improvement for a street driven Mini in its current form - and thus didn't justify the pre-Brexit cost for me.

 

I don't drive my Mini competitively so I don't need even spacing of the gears through 5th. What I do like is the nice spacing 1-4 around town, then the option of a cruising overdrive 5th for the open road.

 

But the current .882 5th of the helical box doesn't really hit the spot as an overdrive cruising gear. For an MPI engined Mini with lots of torque, it would be great to run a 3.44 final drive which would give sparkling performance (with the 5 speed ratios) 1-4, but then 5th doesn't come close to matching the stock 2.76:1 (3.03)

 

Retrofitting a 3.1 FD would yield the desired ~2.7 final ratio, but then 1-3 would be virtually identical to A+ 1-3 gearing (with 2.76:1 FD) and a useful 3.1 4th. But not worth the cost or trouble just to get one useful intermediate gear.

 

Could the .882 5th be replaced with a .80 gear? This is a longshot question and hope, but perhaps a trans authority like Guessworks might have an answer. Not sure how many teeth are on the .882, and whether there is an existing gear that might substitute.

 

The straight-cut version of the box has a .865 5th, but I'm concerned about the noise and I doubt this would make that much difference in terms of cruising (certainly the noise gains would be offset!)

 

Or perhaps I'm overthinking the whole thing, and a 3.03 final drive ratio is still well within comfort. There are a number of situations where the MPI can't pull the 2.76 well (steeper hills at freeway speeds) and the rev/noise difference at ~70mph/110kph isn't that much.

 

Anyway, at the price it I might consider it just as a (bit extravagant) replacement transmission since my original is getting along in miles and is starting to get balky in 2nd... 

 

 

 

Dave



#2 ACDodd

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Posted 13 January 2017 - 11:23 PM

Use a 3.44fd with a 28 tooth a+ input gear will give you 2.9ish in top perfect.

Ac

#3 bluedragon

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Posted 15 January 2017 - 10:54 PM

I hadn't thought about that. I think 29 teeth is standard? I would have to calculate the effect across the ratios but it might be fine. Seems like the 28 tooth gear is fairly uncommon though?

 

 

 

Dave



#4 ACDodd

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Posted 15 January 2017 - 11:44 PM

Fairly easy in the UK.

Ac





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